Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$85.76	3.206%	$88.5095	$88.51	$88.50	$88.50
Purchase #2	$197.98	10.239%	$218.2512	$218.25	$218.25	$218.30
Purchase #3	$199.26	8.220%	$215.6392	$215.64	$215.65	$215.60
Purchase #4	$33.64	6.627%	$35.8693	$35.87	$35.85	$35.90
Purchase #5	$164.27	12.293%	$184.4637	$184.46	$184.45	$184.50
Purchase #6	$110.66	5.117%	$116.3225	$116.32	$116.30	$116.30
Purchase #7	$226.86	12.696%	$255.6621	$255.66	$255.65	$255.70
7 purchase totals =	$1,018.43		$1,114.7175	$1,114.71	$1,114.65	$1,114.80